Radial fans as well as impellers for radial fans are, for example, known from “Strömungsmaschinen” by Klaus Menny, 3rd Edition, B. G. Teubner Stuttgart, 2000. In this application the terms “fan”, “compressor”, “ventilator” or “blower” are used as synonyms. Radial fans are, inter alia, used in ventilators, in particular in CPAP-apparatus.
The CPAP-therapy (continuous positive airway pressure) was developed for the treatment of apneas and is described in Chest. Volume No. 110, pages 1077-1088, October 1996 and in Sleep, Volume No. 19, pages 184-188. A CPAP-apparatus generates, preferably by means of a high-speed, single-stage radial compressor, a positive overpressure up to approximately 30 mbar and administers the same to the respiratory tract of the patient via a hose and a nose mask. This positive pressure is to ensure that the upper respiratory tract remains fully opened during the whole night, so that no apneas will occur (DE 198 49 571 A1).
Suppliers of compressors suited for CPAP-apparatus are, for example, AMETEK, ROTRON, PAPST, ebm, Micronel, Telemeter Electronic. Complete CPAP-apparatus are, for example, distributed by MAP, Weinman or ResMed. It is common that the fan unit is placed in a sound-damping and sound-absorbing box inside the CPAP-apparatus.
Barriers for the use of compressors are primarily the construction size, the weight and the noise development. The construction size and the weight of portable CPAP-apparatus are presently around 5.5 liters and 2.5 kg. The noise development should not exceed 30 dB, as the patients are to have a relaxing sleep beside the apparatus. In order to keep the noise development of known CPAP-fans small, the impeller and the blow-off port of known radial CPAP-fans are offset against each other, i.e. they are not arranged in a plane. A further reduction of the construction size and the weight, e.g. by using smaller compressors, would be desirable.
A maximum air volume of 200 l/min and a maximally achievable pressure of at least 25 mbar (2500 Pa) in the face mask are required for CPAP-apparatus. Pressures around 15 mbar must still allow the conveyance of at least 150 l/min. These requirements apply to conventional respiratory hoses with inner diameters around 20 mm.
Moreover required is a running smoothness, i.e. a small noise development. The radial compressors primarily used so far have to be operated at very high speeds, which results in disturbing whistling sounds.
The company Hörnell developed a welder mask comprising a radial fan from Papst. The fan is fastened on the welder's back by means of a belt. A hose having a diameter of approximately 20 to 30 mm leads from the fan into the top of the welder mask. The fan supplies the welder with 160 liters of fresh air per minute and thus also provides for sufficient cooling.